Abstract

This study aimed to quantify the elongation patterns of the collateral ligaments following TKA during functional activities of daily living. Using mobile video-fluoroscopy to capture radiographic images of the knee in a group of six patients, each with an ultra-congruent knee implant, tibiofemoral kinematics were reconstructed throughout complete cycles of level gait, downhill walking, stair descent, and squat activities. Kinematic data were then used to drive subject-specific multibody knee models to estimate length-change patterns of the LCL as well as three bundles of the MCL. In addition, a sensitivity analysis examined the role of the attachment site in the elongation patterns. Our data indicate a slackening of the LCL but non-uniform length-change patterns across the MCL bundles (ranging from lengthening of the anterior fibers to shortening of the posterior fibers) with increasing knee flexion angle. Near-isometric behavior of the intermediate fibers was observed throughout the entire cycle of the studied activities. These length-change patterns were found to be largely consistent across different activities. Importantly, length-change patterns were critically sensitive to the location of the femoral attachment points relative to the femoral component. Thus, in TKA with ultra-congruent implants, implantation of the femoral component may critically govern post-operative ligament function.

Keywords:
Elongation; Fluoroscopy; LCL; MCL; Multibody model; TKA.

Figures

Figure 1

5

An exemplary pre-operative CT slice…

Figure 1

13

An exemplary pre-operative CT slice (left) together with a subject-specific multi-body model of…

Figure 1

An exemplary pre-operative CT slice (left) together with a subject-specific multi-body model of the knee (right), including the collateral ligament bundles (shown in green) as well as the wrapping surfaces used to prevent penetration of the ligament bundles into the bones (shown in cyan).

Figure 2

5

The ETH moving fluoroscope was…

Figure 2

13

The ETH moving fluoroscope was used to capture radiographic images of the knee…

Figure 2

The ETH moving fluoroscope was used to capture radiographic images of the knee joints throughout a range of dynamic activities (left). An exemplary fluoroscopic image including the implant component projections is shown on the right. Specific informed consents were acquired from the subjects in order to publish their images.

Figure 3

5

Average elongation patterns of the…

Figure 3

13

Average elongation patterns of the LCL and three MCL bundles (solid lines represent…

Figure 3

Average elongation patterns of the LCL and three MCL bundles (solid lines represent inter-subject means and shadings represent ± 1 inter-subject standard deviation). The vertical dotted line represents the average toe-off time for the six subjects.

Figure 4

5

Average length-change patterns of the…

Figure 4

13

Average length-change patterns of the LCL and MCL bundles during five repetitions of…

Figure 4

Average length-change patterns of the LCL and MCL bundles during five repetitions of the level walking, downhill walking, stair descent, and squat plotted against knee flexion angle. Average patterns were calculated only over the flexion ranges achieved by all the subjects during all the trials. Solid lines represent inter-subject means while shading displays ± 1 inter-subject standard deviation.

Figure 5

5

Variation of the maximum length-change…

Figure 5

13

Variation of the maximum length-change of the collateral ligaments during squat for a…

Figure 5

Variation of the maximum length-change of the collateral ligaments during squat for a single subject as a result of moving the femoral (top row) and tibial (bottom row) attachment points in the anteroposterior (left), proximodistal (middle) and mediolateral (right) directions. Solid lines represent the fitted regression lines for LCL (blue), aMCL (dark brown), iMCL (light brown), and pMCL (amber).